1. Field of the Invention
This invention relates generally to flow measurement of particulate streams and in particular to methods for correcting erroneous measurements of particulate streams due to motion other than the motion of particulate matter being measured.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Flow measurement of particulate streams such as wet cakes, grains, cereals, dry powders, minerals, pharmaceuticals, dairy powders, chemicals, spices, snack foods, cement, resins, plastics, fibrous materials, and others is critical to the operation and optimization of a given process. A non-contact flow meter is of great importance since measurements are obtained without interfering with the flow of product through the process transfer line. For flow measurement of some products through transfer lines, this is critical since any obstruction in the line can cause buildup and eventual pluggage. In addition, no degradation of the material occurs since the flow is unobstructed. Also, the integrity of the process is maintained with a non-contact flow meter. For example, with food and pharmaceutical manufacturing, a truly non-contact solids flow meter obtains measurements without any contamination of the process since, being a non-contact device, the integrity of the process is never compromised. This factor is important when considering food, pharmaceutical, mineral, and chemical manufacturing.
Some typical applications for flow/quantity measurements are: feed to dryers, discharge from dryers, feed to milling operations, flow to mixers, flow from dust collectors, flow from conveyors, loading/unloading of railcars, loading/unloading of trucks, loading/unloading of barges, flow of grains through ducts, cement loading/unloading, flow of plastic granules, flow from cyclones, flow in pneumatic transfer lines, loading/unloading of silos, and feed to reactors to mention a few applications.
In U.S. Pat. No. 4,091,385, a Doppler radar flow meter is disclosed in which the flow meter comprises a radar transmitter and receiver that respectively radiates radio waves at a predetermined microwave frequency at least partially through a fluid and receive at least a portion of the radio waves backscattered by at least some of the particulate matter in the path of the radiated radio waves. A signal processor connected to the receiver produces a signal related to the Doppler""s shift in frequency between the backscattered radio waves and the radiated radio waves and, thus, the frequency is related to the velocity of flow of the particulate matter being measured. In particular in this case, the flow meter is used for velocity of flow of fluids such as blood in conduits such as blood vessels.
U.S. Pat. No. 5,550,537 discloses an apparatus for measuring mass flow rate of a moving medium using Doppler radar. The patent discloses a non-intrusive mass flow rate meter that includes a transceiver that transmits an electromagnetic signal of known frequency and power to illuminate a portion of moving material. The transceiver detects the magnitude and the Doppler shift of the electromagnetic signal that is reflected by material moving along the process flow as it passes through the electromagnetic field established by the signal. The transceiver then combines the magnitude of the reflected electromagnetic signal along with the Doppler shift between the frequency of the transmitted and reflected electromagnetic signals to generate an output signal related to the mass flow rate of the material. The problem with the 5,550,537 patent is that only a portion of the moving material is illuminated. This creates errors in the mass flow rate and thus in the quantity of material that is passing through the conduit.
U.S. Pat. No. 5,986,553 issued to the same inventor as the present invention discloses an improved flow meter for measuring solid particulate flow rates by radiating the particulate flow path through a conduit such that substantially all of the particulate matter contributes to and forms backscatter energy. The backscatter energy is used to generate an electrical signal that is proportional to the consolidation of solid particulate matter flowing through the conduit. The flow meter described in U.S. Pat. No. ""553 is quite sensitive to motion and normally very accurate. However, because of its sensitivity to particulate motion it is also sensitive to various xe2x80x9cmotionsxe2x80x9d, other than the particulate material motion, which are often present in a particulate matter distribution system. For example, the motion of a rotating screw conveyor or product dust can be sensed by the system and result in an erroneous indication of the output particulate flow rate.
The present invention discloses a method of compensating and correcting a non-contact mass flow meter which measures the flow of particulate streams through ducts, chutes, or pipes utilizing a Doppler-radar sensor, a unique flow tube, a flow rate and totalizer indicator, and an algorithm to convert the sensor output signal to mass flow rate. For example, in the unique flow meter disclosed in U.S. Pat. No. 5,986,553, the solid particulate matter flows along a first hollow conduit with a second hollow conduit having at least the same diameter as the first conduit and being joined to the first conduit at an angle. At least one sensor is associated with the second hollow conduit and includes a transmitter of electromagnetic energy for radiating the entire particulate matter flow path formed by the first conduit such that substantially all of the particulate matter contributes to and forms backscattered energy. A receiver receives the backscattered energy and generates an electrical signal that is proportional to the concentration of solid particulate matter flowing in the first hollow conduit. A processor is coupled to at least one sensor for generating an output signal representative of the concentration of the solid particulate matter.
In one embodiment described in U.S. Pat. No. 5,986,553, the solid particulate matter flows past the sensor at a substantially constant velocity that is achieved by placing a source of the particulate matter a predetermined distance above the sensor for achieving the substantially constant velocity by gravity flow. In another embodiment described in the ""553 patent, a source of pneumatic pressure is coupled to the first conduit for conveying the particulate matter past the sensor at the substantially constant velocity.
A sightglass is preferably interposed in the second hollow conduit between the sensor and the particulate matter. The electrical signal generated by the receiver is typically a non-linear signal measured in either milliamps or volts. The processor converts the milliamp or volt signal into a pounds-per-hour mass flow rate. A totalizer generates a total quantity value of the material delivered.
The processor includes a memory for storing at least one algorithm for converting the signal generated by the receiver into a continuous range of values to a pounds-per-hour mass flow rate. In the described embodiment, the memory stores a first algorithm for converting a signal generated by the receiver in a first range of values to a pounds-per-hour mass flow rate and stores a second algorithm for converting the signal generated by the receiver in a second continuous range of values to a pounds-per-hour mass flow rate to enhance accuracy of the flow meter.
In the preferred embodiment, the first algorithm has the form of F=aEb (Y=aXb), where F=pounds/hour, E=electrical signals as milliamps or volts, and a and b are constants and the second algorithm has the form of F=a0+a1E+a2E2+a3E3+a4E4 (Y=a0+a1X+a2X2+a3X3+a4X4) were F=pounds/hour, E=milliamps, and a0, a1, a2, a3, and a4 are constants.
Further, a central processing unit is coupled between the receiver and the industrial computer for calculating constants for the first and second algorithms for use by the industrial computer or smart indicator. Alternatively, the processor itself may include a central processing unit for calculating the constants for the first and second algorithms and generating mass flow rate in pound-per-hour. It further may have a converting means in the central processing unit for converting the mass flow rate to total pounds.
The present invention relates to a method of correcting or compensating for erroneous readings of a flow meter of the type disclosed in U.S. Pat. No. ""553 resulting from sensing motion in the system other than motion or movement of the particulate matter.
According to the invention the correction is achieved by generating data points represented by an initial performance curve or initial algorithm under controlled conditions such as in a laboratory. The initial algorithm or performance curve will typically show a relationship between the electrical output signal (typically in milliamps or volts) for different known flow rates. After the flow meter is installed into its working environment the system is operated in its normal manner and at a known flow rate to determine a corresponding electrical signal.
A correction factor is then computed for either the mass flow rate parameter (F) or the electrical signal parameter (E) by using the electrical signal determined at the known flow rate and the initial algorithm.
An adjusted algorithm is then developed by subtracting the correction factor in the initial algorithm. Thus it is seen that sensing motion not actually representing the flow of particulate material may result in a corrected value that can be less than the indicated flow rate such as a situation where the motion of a screw conveyor is the source of error. The corrected value could also be greater than the indicated flow rate as could be the case if the laboratory calibrating process was subjected to backscatter due to grain dust and the grain dust was not present in the final installation. However, the important consideration for either situation is that the laboratory calibration procedure develops an algorithm or a performance curve that represents the flow meter and may be readily adjusted for the particular environment at the final installation. Thus, extensive recalibration is not required even though the individual values of flow rate per unit of sensor output as represented by the initial algorithm or performance curve are substantially different from the flow rate per unit of sensor output as determined from the adjusted algorithm or performance curve.
According to an embodiment for correcting the machinery motion, the system is operated at a zero flow rate to determine a flow rate correction factor at a specific electrical signal value, and according to a preferred embodiment for correcting for dust, etc., the system is operated at a known positive flow rate to obtain an electrical signal correction factor at a specific flow rate.